Hydraulic elevator control



June 8, 1965 Filed Sept. 6, 1961 FLUID CHAMBER J. F. M NAIR EI'ALHYDRAULIC ELEVATOR CONTROL 4 Sheets-Sheet 1 LEVELING VALVES um i \66 T0FLUID SINK sYmHRo ELECTRICAL CONTROL MEANS 26 I UP-VALVE/ VALVE MEANSHYDRAULIC CONTROL gm \28 -C|RCUIT DOWN VALVE \24 I 70/ MEANS SELECTOR 74INVENTORS A JAMES F. MAC NAIR BY PETER J. SCULLY ATTORNEY June 8, 1965Filed Sept. 6, 1961 J. F. M NAIR EIAL HYDRAULIC ELEVATOR CONTROL 4Sheets-Sheet 2 IE 7 I, a T

J Li.) ii? 2 #5 i E g: i E

1:33 mfg [:lg mfg 1:1 mfg [:2 g [mfg x g T] 72 INVENTORS JAMES F. MACNAIR [F BY PETER J. SCULLY H m AW M ATTORNEY June 8, 1965 J. F. M NAIREI'AL HYDRAULIC ELEVATOR CONTROL 4 Sheets-Sheet 3 Filed Sept 6. 1961220V 60 CPS 1 U MM S A v U E T.. Ul B Du 5 DM 8 1. U 2 U D s U YA ;V X Dl s w L U .l X M U w L L V F A D U. S s U U L1 F XDZ DSA INVENTORS F.MAC NAIR J. SCULLY JA MES PETER ATTORNEY DAL LJ United States PatentYork Filed Sept. 6, 1961, Ser. No. 136,275 11 Claims. (Cl. 1137-69) Thisinvention relates in general to hydraulic elevator controls and inparticular to an automatic speed control system which provides overspeedprotection, speed equalization, and smooth acceleration and decelerationin hydraulic elevator installations. The invention can be utilized inany hydraulic elevator system, but it is particularly useful inautomatic elevator control systems such as described, for example, inUS. Patent Number 2,913,- 070, which was issued on November 17, 1959, toMagnus N. Nyberg for an Automatic Elevator Control.

Hydraulic elevator systems were superseded forty years ago by electricelevator systems, which are much smoother in operation and much easierto control than their hydraulic counterparts. Before this happened,however, many large buildings were erected all over the World withhydraulic elevator systems, and a large number of these hydraulicelevator systems are still in operation today. In New York City alonethere are approximately 300 buildings which use hydraulic elevatorsystems. As it happens, the structural requirements for hydraulicelevators diifer so radically from those for electric elevators thatthese installations cannot be changed without major structuralalterations in the entire building. In most cases the necessarystructural alterations are out of the question, for one reason oranother, so that these hydraulic elevator systems will stay in serviceuntil their buildings are torn down and rebuilt. Therefore anyimprovements or modernization of the elevator service in these buildingsmust be made by improving the hydraulic elevator systems therein ratherthan replacing them with electric systems.

One such improvement is described in the above noted US. Patent Number2,913,070, which discloses an automatic electric control circuit thatreplaces the cumbersome, slow acting, mechanical control systemsformerly used in hydraulic elevator systems. This automatic controlsystem obviates the requirement for skilled operators, and provides acompletely automatic control system, which can be operated by thepassengers if desired. But although this automatic control system was avast improvement over manual control systems, it was by no meansperfect. It delivered the passengers to their selected floors, but itgave them a rough, jarring ride in transit, particularly in thedeceleration period when the elevator was approaching the selectedfloor. Furthermore, the system did not provide any means for equalizingelevator speed under different load conditions, whereby a heavily loadedcar would move up like a snail and down like a rock while a lightlyloaded car would do the opposite. In addition, the system did notprovide for overspeed protection and the elevator cars were thereforeliable to build up so much speed as to frighten the passengers, to givethem a severe jolt when the car stopped, and to overshoot the selectedstop.

This invention is addressed to the problems which were unsolved in theseprior art improvementsthe problems of 1) equalizing speed under varyingload conditions, (2) providing smooth, effective overspeed protection,and (3) providing smooth acceleration and deceleration. Many differentmethods have been used in the past in an attempt to solve theseproblems, but none of these prior art methods have proved workable inpractice. For example, some prior art systems have tried to equalizespeed by counting the number of passengers entering a car and thenselecting a hydraulic drive setting based on the number of persons inthe car multiplied by their hypothetical average weight. The passengerswere counted by a photocell counter circuit in the car, and thehydraulic drive setting was selected in a variable hydraulic drivecircuit which could be adjusted in predetermined increments in responseto a signal from the photocell counter. This system, however, was anapproximation at best, and in practice it was subject to grave defects.In the first place, it was relatively complex in structure and itscomplexity encouraged circuit failure or mis-operation. In the secondplace, errors were cumulative in the circuit. If the counter added acount, as counters sometimes do, these erroneous counts would accumulatefrom one trip to the next until the counter would indicate a fullcondition on an empty car. This, of course, produced a worse ride thanan unequalized drive system. And finally, the counter method ofequalization was not useful in solving the other two problems-smoothingdeceleration and providing overspeed protection.

The deceleration problem has, in the prior art, been approached by aspeed increment system similar to those used in the prior art speedequalizing systems. The speed of the car was decreased by timedincrements instead of by a sudden switch from top speed to approachspeed. This method, however, was also relatively complex in structureand relatively unreliable in operation. In practice it multiplied thenumber of jolts instead of producing a smooth transition from high speedto approach speed, and it complicated the problem of reaching thecorrect approach speed to achieve exact leveling without overshoot.Since the reduction of speed was timed in accordance with a hypotheticalaverage car speed, the deceleration was too fast on slow moving cars andtoo slow on fast moving cars. Furthermore, this speed increment systemmade no contribution to overspeed protection.

The prior art approach to overspeed protection was based on a governorwhich was coupled between the elevator drive shaft and the hydraulicvalves which controlled the movement of the drive shaft.

of the drive shaft increased the governor would close the p h draulicvalves via a mechanical linkage and as the s eed of the drive shaftdecreased the governor would open the hydraulic valves. This method,however, was unsatisfactory in practice because it takes much more forceto close a hydraulic valve than it does to open the valve.

Therefore when the governor cut in the car would slow 7 down with a joltand then accelerate slowly until the governor cut .in again, whereuponthe car would slow down with another jolt. This produced a veryunpleasant sensation, particularly on long rides in a heavily loadedcar.

Other methods of solving the problems of speed equalization, smoothdeceleration, and overspeed protection As the speed rnatic elevatorcontrol system of that type.

and 2 the structural elements numbered ltl through 68 have been proposedin the past, but in general they have all suffered from the above noteddisadvantages-Le. they have applied to only one of the three problemsinstead of to all three, they have been unduly complex in nature andunreliable in operation, they have been based on hypotheticalquantities, and they have not provided an adequate solution to theirparticular one of the three problems let alone to all three at once. Inaddition to these disadvantages, the prior artspeed control systems havesuifered from a more serious handicap in that their action was based onfactors which vary from elevator to elevator, whereby each speed controlsystem had to be tailor made for its particular application.

, Accordingly, one object of this invention is to prov-ide a hydraulicelevator control system which provides overspeed protection, speedequalization, and smooth deceleration in hydraulic elevatorinstallations.

Another object of this invention is to provide an automatic speedcontrol system which simultaneously provides overspeed protection, speedequalization, and smooth deceleration in hydraulic elevatorinstallations.

A further object of this invention is to provide an automatic speedcontrol system of the above noted type which is simpler in structure andmore reliable in operation than those heretofore known in the art.

An additional object of this invention is to provide an automatic speedcontrol system of the above noted type which is smoother in operationand more effective than those heretofore known in the art.

Another object of this invention is to provide an automatic speedcontrol system of the above noted type which can be applied to widelyvarying elevator installations without any significant changes in theautomatic speed control circuit or in the elevator system.

A further object of this invention is to provide an automatic speedcontrol system of the above noted type which is less expensive tomanufacture, easier to install, and easier to maintain than thoseheretofore known in the art.

Other objects and advantages of this invention will be apparent to thoseskilled in the art from the following description of one specificembodiment, as illustrated in the attached drawings, in which:

MG. 1 is a block diagram of one illustrative hydraulic elevator andautomatic elevator control system incorporating the automatic speedcontrol of this invention;

FIG. 2 is an elevation section of one illustrative selector switchrneans and hydraulic control means for the elevator system of FIG. 1;

FIG. 3 is a schematic diagram showing one illustrative arrangement ofbrushes and brush wipers for the selector switch means shown in FIG. 2;

FIG. 4a is a schematic diagram of one portion of an illustrative circuitarrangement for the valve control circuit of PEG. 1;

FIG. 4b is a schematic diagram of the remaining portions of the circuitshown in PEG. 4a; and

FIG. 5 is a schematic diagram of the speed correction circuit.

Although the speed control system of this invention can be used with anyhydraulic elevator, it is particularly useful in connection withhydraulic elevators containing automatic control systems, such asdisclosed in the above noted U.S. Patent Number 2,913,070, and thisinvention will therefore bedescribed in connection with an autoln FEGS.1

are identical with the structural elements disclosed in FIGS. 1 and 2 ofthe above noted US. Patent Number 2,913,070, except for valves 24c, 24d,26c, and 26d, and the structural elements numbered ill through 92 and24c, 24d, 26c, and 26d correspond to the novel structure of thisinvention. e

The prior art portions of FIG. 1 show a hydraulic elevator system inwhich an elevator car N is positioned up and down an elevator shaft bymeans of a hydraulic ram'lz. As the elevator car ltl moves from floor tofloor a synchro generator 14, which is coupled to a counterweight pulleyshaft 16, feeds back signals to synchro motor 18 indicating the actualinstantaneous elevation of the elevator car. When an operator wishes tomove the elevator to a different floor, he depresses the push buttonassociated with the desired floor on a iloor selector panel 2%, whichgenerates a signal indicating the selected floor. This signal is coupledto electrical control means 22. At the same time, synchro motor 13transmits a signal to electrical control means 22 indicating the presentlevel of the elevator car llt These two signals are compared in theelectrical control means 22 and if the selected floor is below thepresent position of the elevator car, the down valve means 24. will beenergized, causing the hydraulic control means 2% to bleed fluid fromthe hydraulic ram 12, thus moving the car downward. When the elevatorcar reaches the selected floor, the electrical control means 22de-energizes the down valve means 24- and the hydraulic ram stops. If,on the other hand, the selected floor is above the present level of theelevator car, the electrical control means will energize the up valvemeans 26. l-lydraulic control means 238 will then feed fluid into bydraulic ram 12, and the elevator car will start on an upward motion;This upward motion continues until the selected floor and the indicatedfloor are the same. At this time the up valve means 26 is de-energizedand the hydraulic ram stops.

in accordance with the novel features of this invention the speed of theelevator car ltl is controlled by means of a valve control circuit illwhich is coupled between electrical control means 22 and valve means 24and 26. Valve control circuit 7d receives a signal indicating theelevator cars actual speed of movement from a tachometer 72 which isalso coupled to counterweight pulley shaft 16. Valve control circuit 7dalso receives signals indicating the actual state of hydraulic controlmeans 2% from selector switch means 74 which is mechanically coupled to,the movable part of hydraulic control means Valve control circuit 7t?also receives signals from electric control means 22, which selects thedirection movement and the starting and stopping times as in the priorart. Valve control circuit 7d is adapted to correlate 7 these variousinput signals in such manner as to provide equalization of speed undervarying loads, smooth acceleration and deceleration, and overspeedprotection as will be described in greater detail below.

PlGQZ shows one illustrative hydraulic control means, up and down valvemeans, and selector switch means which can be used in the elevatorsystem illustrated in FIG. 1. The structural elements numbered 112through 63 are identical with the structural elements disclosed anddescribed in the above noted US. Patent Number 2,913,079, except forvalves 24c, 24d, Zdc, and 26d and the structural elements numbered 74through 92 and 1234a, Ede and 26d are the novel structure of thisinvention. .The numbers on the prior art elements in FIG. 2 are the sameas tho'seused in the above noted patent and the function of these priorart elements is identical in this invention whereby the descriptiongiven on columns 2 and 3 of the above noted patent will be valid exceptfor the modifications noted below. In the prior art portions of thestructure, hydraulic fluid is driven I into hydraulic ram i2 when valvestem is moved downward from the neutral position shown in 2', andhydraulic fluid is bled from hydraulic ram 12 when valve stem M is movedupward from its neutral position.

The position of valve stem 4% is controlled by solenoid operated valvesil lb, 26a, andildb, which operate in CODJURCUOH with a pilot valve 32to control the fluid pressure in fluid chamber 36. In the upwardposition of valve stem id, pilot valve 32 is positioned so as to open aiiuid conduction path between Valve ports 52 and].

. 5 56 thereof, which connects conduit 57 to conduit 68. In the downwardposition of valve stem at), pilot valve 32 is positioned so as to open afluid conduction path between valve ports 52 and 54 thereof. Thisconnects conduit 57 to conduit 53. In the neutral position of valve stem4%), pilot valve 32 is also positioned in a neutral position, i.e. aposition in which valve port 52 is closed so that conduit 57 is notcoupled to either of the other two conduits. When valves 24a, 24b, 26a,and 26b are de-energized, valve stem 46 will be driven to its neutralposition by the action of pilot valve 32, which will couple the fluidsource to fluid chamber 3-6 if valve stem 49 is above its neutralposition and which will couple the fluid sink to fluid chamber 36 ifvalve stem dil is below its neutral position.

To raise elevator car 1%, the valve stem 4% of the hydraulic valvecontrol means is moved to its downward position by energizing solenoidvalve 26a and 26!). Valve 26a introduces fluid from the fluid sourceinto fluid chamber 36 and thus drives valve stem 40 downward. (The fluidsink is isolated from conduit 58 by valve 2612, which is closed in theenergized state thereof.) When solenoid valve 26a and 26b arede-energized, valve 26b couples the fluid sink to fluid chamber 36 viaconduit 58, valve ports 54 and 52, and conduit 57, thus moving valvestem 40 upward to its neutral position. To lower elevator car 19,solenoid valves 24a and Zeb are energized, which couples the fluid sinkto fluid chamber 36 through valve 24a, thus driving valve stem 46upward. When solenoids 24a and 2412 are de-energized, the fluid sourceis coupled to fluid chamber 36 via conduit 68, valve ports 56 and 52,and conduit 57.

It can be seen, then, that the up and down valve means operate in pairs,the normally closed member of the pair acting to couple either the fluidsource or the fluid sink to fluid chamber 36 to initiate the upward ordownward movement of valve stem i0, and the normally open member of thepair acting to reverse the coupling and re-center valve stem 4-!) whenthe valves are de energized. in this prior art arrangement, thehydraulic control means is driven either to its full open or full closedposition by the up and down valve means, and is held in a neutralposition in the absence of a signal to either the up or down valvemeans. In accordance with this invention, however, novel structure isadded to partially open and partially close the hydraulic valve means toachieve slow acceleration or deceleration and also to move valve stem 49upwardly or downwardly to compensate for overspeed or to decelerate theelevator in the approached zone. This is done quite simply by addingsmall solenoid valves 24c, 24d, 25c, and 26a in parallel with the priorart control valve and by coupling selector switch 74 to valve stem 46 todetermine the actual position thereof. In this particular embodiment ofthe invention, the selector switch comprises a stationary plate 76containing brushes and brush wipers and a movable plate 78 containingbrushes and brush Wipers which engage the brushes and brush wipers onplate 76. The brushes and brush wipers are indicated schematically inFIG. 2 by the tooth-like projections on the surface of plates 76 and 78.Movable plate 73 is coupled via pulleys 8i) and S2-to the top of valvestem 40 and therefore moves up and down in synchronism with the movementof valve stem 40. The brushes and brush wipers on plates 76 and '78 areadapted to provide signals which indicate the approximate speed of theelevator car and these signals are used to control valve control circuit79 to approximate the desired speed conditions.

In accordance with this invention valves 26a and 2512 are only energizedduring the high acceleration portion of the upward or downward travel.As soon as valve stem 46 reaches a position indicating that top speed isbeing approached, valve 26a (or 24:!) is cut out or" the circuit and isreplaced by smaller valve 26c (or Ma) til for the duration of the upwardor downward travel. Since valves 24c and 260 are smaller than valves24:: and 26a, the acceleration will continue at a much slower rate whentop speed is approached. If the top speed is exceeded during the upwardor downward travel, valves 2 5d or are opened, by valve control circuit70, until the speed of elevator car 1% drops back to its rated topspeed. The circuit that opens valves 24d and 25d is responsive totachometer 72, which measures the actual speed of elevator car 16. Whenelevator car It is near its selected fioor, the valves are de-energizedand normally open valves 24b or 2615 return valve stem 49 toward itsneutral position until the desired approach speed is reached. If theelevator car does not come down to its proper approach speed, valves 24dor 26d will be opened again to decelerate down to the proper speed sothat the elevator car will not overshoot the selected floor. If theelevator car is traveling at or slightly below its rated top speed itwill decelerate smoothly down to the proper approach speed without anyopening of valves 24in or And if the elevator car reaches the properapproach speed before it comes into the leveling zone,

which extends one foot above and below the desired level, the elevatorcar will come to rest at the desired level without any overshoot.

it should be noted here that the tachometer means could be used byitself to perform the above noted functions, but that the combination ofa tachometer with a selector switch is preferable because it provides asignificant simplification in the valve control circuit. The position ofthe brushes on the selector switch does not indicate the exact speed or"the elevator car, since the exact speed varies as a function of load,but the position of the brushes will indicate the approximate speedwithin a relatively large but predetermined tolerance. Therefore thevalve stem of the hydraulic control means can be positioned to anapproximately correct position by a simple switching circuit which isresponsive to the selector switch, and any errors due to a change in theload condition can be corrected in an equally simple correction circuitwhich is responsive to the tachometer. This combination provides thedesirable objectives of smooth acceleration and deceleration, speedequalization, and overspeed protection without the drawbacks of complexand unreliable control circuits. It should be understood, however, thatthe selector switch and its associated circuits could be usedindependently of the tachometer and its associated circuits if desired,and that the tachometer and its associated circuits could also be usedindependently of the selector switch and its associated circuits. In itsbasic form, this invention comprises (1) a novel approximate speedcontrol device comprising the selector switch and its associatedstructural elements, (2) a novel speed correction device comprising thetachometer and its associated structural elements, and (3) a novelautomatic speed control system comprising the selector switch, thetachometer, and their associated structural elements.

7 FIG. 3 shows one illustrative layout for the brushes and brush wipersof selector switch 74 in this particular embodiment of the invention.There are two symmetrical sets of brushes on movable plate 8; one setcorresponding to the up direction of elevator travel, and the other setcorresponding to the down direction of elevator travel. The up brushesare indicated by the letter U in their designation while the downbrushes are indicated by the letter D in their designation. Stationaryplate 76 contains a single set of brushes and brush wipers which areadapted to engage the up brushes of movable plate 73 when the elevatoris moving upward and to engage the down brushes of movable plate 78 whenthe elevator is moving downward. The brushes and their correspondingwipers are adapted to make and break contact at predeterminedapproximate speeds. The approximate speed is, of course, directlyrelated to the position of the hydraulic valve means, although the exactrelationship might difler in aromas some elevator installations. Thisrelationship, however, can be easily determined by well known prior arttechniques so that the brushes can be set to make or break at anydesired approximate speed. 7

FIGS. 4a and 4b show one illustrative circuit which can be used toembody valve control circuit 7% with the particular selector switchlayout shown in FIG. 3. in the circuit of PEG. 4a, the relay contactsmarked UM, BM, SP, LV, and APP are actuated by relays in electricalcontrol means 22 or in the elevator shaft. All of the other contacts areactuated by relays shown in PEG. 412. Electrical control circuit 22 canbe any suitable prior art elevator control circuit which provides thefollowing signal inputs to toe valve control circuit of this invention:(1) an up signal indicating that the elevator car is to begin movingupward (this signal actuates all of the UM contacts shown in FIG. 4a);(2) a down signal indicating that the elevator car is to begin movingdownward (this signal actuates all of the DM contacts shown in FIG. 4a);a high speed signal indicating the elevator car is to make a long run(this signal actuates the Si contacts shown in EEG. 4a); a low speedsignal indicating that the elevator car is to make a short run(thissignal momentarily actuates the SP contacts shown in MG. 4); a highspeed approach zone signal indicating that the elevator car has reachedthe approach zone for its selected floor under high speed conditions(this signal de-actuates the SP contacts shown in FIG. 4a); a low speedapproach zone signal indicatin g that the elevator car has reached theapproach zone for its selected floor under low speed conditions (thissignal actuates the AP? contacts shown in FIG. 4a); and a leveling zonesignal indicating that the elevator car has reached the leveling zonefor its selected floor (this signal actuates the LV contacts shown inFlG. 4a). in addition to these input signals from electrical controlmeans 22, the valve control circuit of FIG. 4b also receives an inputsignal from tachometer T2 and several inputs from selector switch '74,whose individual brushes and brush wipers are identified by the samedesignations used in FIG. 3. The relay contacts and brushes areseparated from their solenoids in FIG. 4a and FIG. 4b for clarity ofillustration, but it will be understoodby those skilled in the art thatcontacts with the same designation are actuated simultaneously by thesolenoid having the corresponding designation.

in describing the overall operation of the valve control circuit, itwill be useful to first describe the speed correction portions of thecircuit and then to present some exemplary sequences of operation forthe circuit as a whole. Referring to FIG. 5, tachometer is coupled torelay meters 84, $6, and M, which can comprise any suitable prior artrelay meter such as the Simpson model 29X voltmeter or the like. Eachrelay meter has a coil, which is indicated in FIG. 5 by the resistorwithin the box denoting the relay meter, and a relay contact circuitcomprising the needle of the meter and two stationary contacts which canbe adjusted to contact the needle of the meter at any predeterminedpoint in its positive or negative direction of travel. The needle of themeter rests in the center position in the absence of a voltage input andtravels either to the right or to the left when a voltage is appliedthereto, depending upon the polarity of the voltage. The defied tien ofthe needle, of course, is proportional to the magnitude of the appliedvoltage. The coils of all three relay meters are coupled in parallel totachometer '72, which can be anysuitable tachometer generator thatproduces a DC. voltage output proportional to its speed of rotation. The scales of the relay meters are preferably calibrated in arms of speedrather than voltage to facilitate adjustment of the stationary contactsto intercept the needle at any d sired speed.

'l'n this particular embodimentof the invention, relay meter is adaptedto close its contacts when the elevator reaches its normal runningspeed; relay meter 36 is adapted to close its contacts Whenthe elevatorreaches its normal approach speed; and relay meter 34 is adapted toclose its contacts when the'elevator exceeds its maxivmum speed. Thespecific values of these speeds will, of

course, depend upon the particular elevator installation for which thecircuit is designed, so that the exact speed values cannot be specifiedin general. For purposes of explanation, however, it will be assumedthat relay meter 88 is set to close at a speed of 460 feet per minute,and that relay meter 36 is set to close at feet per minute, and thatrelay metertld is set to close at 440 feet per minute. The operation or"the relay meters and their associated circuits can be best described byrunning through atypical operating cycle thereof. Assume that an upsignal or a down signal is received from electrical control means 22 toinitiate an upward or a downward movement of the elevator. The up ordown signal actuates all of the UM or DM contacts in the valve controlcircuit, whereby voltage is applied to rectifier all by Way of contactsUM or DM thereby developing a positive DC. voltage on the needle of eachrelay meter and a negative DC. voltage on the solenoid circuits coupledto the stationary contacts of the relay meters. Other UM or DM contactsactuate the up or down valve means, and the elevator starts to move inthe specified direction. When the elevator begins its motion, tachometer'72 starts to devedop a voltage output proportional to the instantaneousspeed of the elevator. As the speed of the elevator rises, the outputvoltage of tachometer '72 rises unti the elevator reaches its normalrunning speed of 400 feet per minute, at which time the contacts ofrelay meter its close. (Relay meter 86, which closes at 110 feet perminute, is initially removed from the circuit by normally open contactsVSU and VSD which do not close until the elevator is decelerating to itsapproach speed.) When the contacts of relay meter 88 close, solenoidTAO?) is energized via diode D1, normally closed contacts TACD andnormally closed contacts TAC3 As soon as solenoid TACS is actuated itshuts itself oil by opening normally closed contacts TAC3 A resistor Rland capacitor Cl are coupled in parallel with solenoid TAC3 to hold thesolenoid energized momentarily after its circuit is broken by theopening of contacts TAC3 Capacitor Cl. stores electrical energy whilecontacts TAC3 are closed and discharges its energy as soon as they open.The time constant of this RC circuit is chosen to hold solenoid TACSenergized long enough to allow solenoid TAC4 to be energized by normallyopen contacts TAC3 After energizing solenoid TACd, solenoid TACEl isdc-energized by the discharge of capacitor Cit while solenoid TAC llatches itself closed by means of contacts TACdg and also opens thecircuit to-the coil of relay meter and to the solenoid of TAC3 throughnormally closed contacts TACd and TAC4 The diode Dll in series withsolenoid TAG? protects relay meter 83 and rectifier t ll from theinductivekickback voltage which arises when the current through solenoidTAC3 is interrupted. Resistor R1 and capacitor C1 further reduce theinductive kickback by smoothing the transiston between the energized anddeenergized states of the solenoid. In summary, the closure of relaymeter 83 acts to energize solenoid TACd, which indicates that theelevator has reached its normal running speed, and to remove relay meter88 from the circuit for the duration of the elevator run to protect itscontacts from being overloaded. The actuation of solenoid TACd switchesother circuits that terminate motion in the hydraulic control means totheoretically hold the elevator at its normal running speed.

In certain circumstances, however, the elevator may continue toaccelerate after having reached its normal running speed until itexceeds its maximum speed of 440 feet per minute This occurs, forexample, in a heavily loaded car which is moving downwardly. When themaximum speed is reached, the contacts of relay meter 34 will close,which will momentarily energize solenoid TAC through diode D2 andnormally closed contacts TAC Before solenoid TAC has time to energize,however, the

Q voltage applied through diode D2 will be coupled directly to capacitorC2 through normally closed contacts TAC This will charge capacitor C2 upto the full value of the DC. output voltage of rectifier 9%. When thecontacts of solenoid TAC close, however, the solenoid circuit isimmediately broken by the opening of contacts TAC and capacitor C2 iscoupled to resistors R2 and R3 by the opening of contacts TAC2.Capacitor C2 then discharges through resistors R2 and R3 to holdsolenoid TAC in the energized conditions for some predetermined lengthof time which is controlled by the setting of R3. When capacitorCZ hasdischarged, solenoid TAC will be deenergized, but as soon as it returnsto the de-energized state it will be immediately re-energized if thecontacts of relay meter 84 are stillclosed. (Diode D2 protects relaymeter hdandrectifier 9% from inductive kickback.) Thus solenoid TAC willproduce periodic pulses as lon as the contacts of relay meter 84 remainclosed. The time duration of these pulses is adjustable within areasonable range by the setting of variable 'resistorRB. This pulsationis transferred to solenoid TAC2 by means of contacts TAC so thatsolenoid TAC2 will also produce periodic pulses of a predetermined timeduration as long as the contacts of relay meter 84 remain closed.(Resistor R4 protects the contacts of relay meter 84 when they open.)The pulsations of TAC2 are coupled to the elevator speed reduction valvedescribed previously, and each pulse serves to reduce the speed of theelevator by a speed increment which is proportional to the duration ofthe pulse. Thus the pulses will reduce the elevators speed by smallincrements until it falls below the rated top speed of 440 feet perminute at which time the contacts of relay meter 84 Will open again andthe pulsations will cease.

The frequency of the above described pulsations is determined jointly bythe response time of relays TAC and TAC2 and the pulse duration selectedby the setting of adjustable resistor R3. It is not possible to specifythe exact frequency or pulse duration of the circuit, however, becausethe best frequency and pulse duration will be determined by theparticular hydraulic valve means used in connection With the circuit andthe particular elevator system with which the elevator is used. Itshould be noted, however, that a pulsating overspeed protection circuitis not essential to the basic form of this invention. The pulsatingcircuit of this particular embodiment is used to protect the meter relaycontacts from being welded by inductive kickback current when relay TACis de-energized. With the pulsating meter circuit, the relay metercontacts only act to make the TAC relay circuit, which then breaksitself. This protects the relay meter contacts from the inductivekickback current. if a buffer amplifier is coupled between the meterrelay contacts and the TAC relay, however, relay TAC could be energizedcontinuously as long as the meter relay contacts remain closed. Theoverspeed circuit would op-' crate in the manner described above exceptthat the elevator would be decelerated continuously until it drops belowits maximum speed instead of being decelerated in pulses. The abovedescribed overspeed circuits can be mechanized by many other suitablecircuit arrangements which will be apparent to those skilled in the art.For

example, the relay meters could be replaced by electronic thresholdcircuits of one type or another, and the relays could be replaced byflip-flops if desired.

Due to the action of the above described overspeed circuit, the elevatorwill be traveling somewhere between its normal running speed of 400 feetper minute and its maximum speed of 440 feet per minute when it entersthe approach zone for its selected floor. In this particular example theapproach zone extends for approximately 15 feet above and below theselected floor level. When the elevator enters the approach zone for itsselected floor, a set of approach contacts close in the elevator shaftand a decelerate signal is generated by electrical control means 22 toinitiate deceleration to the approach speed of feet per minute. In thevalve control circuit this decelerate signal returns all of the SPcontacts to their normal condition, which begins a smooth decelerationprocess in the hydraulic control means. At the time the elevator shouldhave theoretically reached its approach speed, the VSU or VSD relay isenergized, which closes the circuit to the coil of relay meter 86through normally closed contacts SP and normally open contacts VSU orVSD If the elevator is going faster than its desired approach speed, thecontacts of relay meter 86 will close and the elevator will be pulseddown to its approach speed by the same pulser circuit which was used tolimit the elevators maximum speed. The elevator will then come into itsleveling zone at the correct approach speed so that it will come to restat its selected floor level without overshoot. The leveling zone in thisparticular example extends approximately one foot above and below theselected iioor level. When the elevator comes into the leveling zone theUM or DM and VSU or VSD contacts return to their normal condition andsolenoid TACd is de-energized. This returns the valve control circuit toits original condition and the hydraulic control means then returns toits neutral position, thus smoothly decelerating the elevator from itsapproach speed to a stop at the selected floor.

The other portions of the valve control circuit can also be bestexplained by running through some illustrative el vator operating cycle.Assume, for example, that the elevator receives a signal from electricalcontrol circuit 22 indicating that the elevator car is to move upward ona long run (two or more floors). This signal actuates all of the UM andSP contacts shown in the circuitry of FIG. 4a. The first effect of theseclosures is to apply power to all of the solenoid circuits throughnormally open contacts UM and to energize solenoids UF, UFA, and USAthrough their respective UM and SP contacts. These solenoids in turnenergize control valves 26a, 26b, and Zea, which start the elevatormoving upward at a relatively high rate of acceleration. In thisparticular embodiment of the invention, the CU contacts of selectorswitch '74 break when the elevator reaches a speed of approximately 300feet per minute, thereby dc energizing solenoid UFA and dropping out thelarge valve 26a (FIG. 2), thus reducing the elevators rate of acceleration. The elevator then continues to accelerate toward the normalrunning speed but at a slower rate which is determined by the size ofsmall valve 250. When the elevators speed reaches approximately 360 feetper minute, contacts DU of selector switch 74 make up, therebyenergizing solenoid UP which latches itself closed via normally opencontacts UP Solenoid UP provides an extra measure of overspeedprotection for the circuit. If, for example, a short were to existaround the CU brushes of selector switch 7 5, the UFA solenoid would notdrop out when it was supposed to and the elevator would continue toincrease its speed at a high rate of acceleration. This possibility isprecluded by the opening of normally closed contacts UP which willdc-energize the UFA solenoid even if the CU brushes are shorted.Solenoid UP also energizes solenoid HS, which latches itself closedthrough normally open contacts H8 Solenoid HS acts to open up thecircuit to the single floor (slow speed) solenoids X, XU, and XD so thatthey will be removed from the circuit in a high speed run. TheX, XU, andXD solenoids are only used on single floor runs, which will be describedlater.

After the DU contactshave made up, the elevator continues to accelerateat a low rate of acceleration until it reaches it normal running speedof 400 feet per minute at which time solenoid TACd will be energized byrelay meter 88 as described previously. When solenoid TAC4 is energized,solenoid UAL will be energized via normally open contacts TAC4 and UMand this will deenergize solenoid USA by opening normally closedcontacts UAL As a safety measure, normally closed consci a with solenoidUFA to the CU brushes should tacts UAL are added in de-energize thissolenoid in case be short circuited and the DU brushes or the UPsolenoid in position so as to terminate all acceleration due to movementof the hydraulic control means. Under ideal conditions this would holdthe elevator at its normal running. speed of 400 feet per minute.

But suppose, for one reason or another, that the ole vator continues toaccelerate after it has reached its normal running speed and that itsspeed exceeds the maximum speed of 440 feet per minute. This can happenwhen an empty car is moved upwardly, or when a fully loaded car is moveddownwardly, or when leakage develops in normally closed valves or 26a.in this case the pulsating overspeed circuit will be actuated andsolenoid TACZ will pulsate as long as the overspeed condition persists.The pulsation of solenoid TACZ will actuate solenoid USD via normallyopening contacts TAC2 and the pulsations of solenoid USD will pulsatethe hydraulic decelerating valve 2nd by means of normally open contactsUSD and USD The elevator will then be decelerated by predeterminedincrements until it has fallen below the maximum speed, at which timethe pulsations will terminate. The overspeed circuit will cut in asoften as necessary to hold the elevator below its maximum speed duringthe run.

When the elevator reaches the approach zone for its selected floor, allof the SF contacts will return to their normal condition, in response toa signal from electrical control means 22, and solenoid UP will beole-energized, thereby de-energizing control valve 26b. When controlvalve 26b is de-energized the elevator starts to decelerate 7 downtoward its approach speed, and the deceleration process is stopped byre-energizing solenoid UF when the approximate approach speed isreached. Solenoid UP is re-e nergized through normally open contacts VSUwhich are actuated by the closure of the EU contacts on selector switchmeans '74. The EU contacts are set to make at approximately 280 feet perminute, but since the hydraulic valve means is in motion when the EUcontacts make, and since a certain amount of time is required to closethe contacts of solenoid VSU, the elevator speed should under normalconditions be decelerated down to about 110 feet per minute when the UPsolenoid is re-energized. The UP solenoid re-energizes hydraulic controlvalve 26b to terminate deceleration of the elevator. If the elevatorspeed is above 110 feet per minute when the deceleration period isterminated, however, the elevator will be pulsed down to the correctapproach speed by means of solenoid USD and solenoid TACZ, which will bepulsed by relay meter as until the elevator drops below the correctapproach speed.

When the elevator comes into its leveling zone, solenoid 22-, and alevel sensor in the elevator shaft. The level sensor can comprise anysuitable prior art device, as for example the level sensor described insaid U. S. Patent Number 2,913,070. The leveling valves can comprise anysuitable prior art valve arrangement for adding a small amount of fluidto or bleeding a small amount of fluid from hydraulic ram 12 whenhydraulic control means 23 is in its neutral position. (it will benoted, in FIG. 2, that conduit )2 is coupled directly to hydraulic ram12 in the neutral position of valve stem id.) The leveling valve controlcircuit can comprise any suitable circuit adapted to switch conduit 92to the fluid source when the elevator car is below its desired level, asindi cated by the output of the level sensor, and to switch conduit @2to the fluid sink when the elevator car is above its desired level. Theexact details of the level sensor, leveling valves, and leveling valvecontrol circuit will not be disclosed in. this document, since thisinvention is concerned with speed control rather than with leveling, butleveling systems of this type are well known to those skilled in the artand any suitable prior art leveling systems can be used in connectionwith this invention.

For a high speed run in the down direction, the above described cycle ofoperation is identical except for direction. Motion in the downwarddirection is controlled by down direction solenoids VSD, DP, DSA, BSD,DPA and DAL. Each of these down direction relays is analogous to thecorrespondingup direction relay described above and each connected in anidentical contact circuit to duplicate the above described sequence ofoperation for long runs in the down direction. The relay meter circuits,of course operate the same for either the upward or downward directionof travel.

On short runs in the up or down direction, the operation of the up anddown relays is controlled by the XU, XD, and X relays shown in FIG. 4b.As mentioned earlier, a hort run is initiated by momentarily closing the8? contacts and permanently closing either the UM or DM contactsdepending on whether the short run is in the up or down direction. Whenthe SP contacts are momentarily closed, solenoids XU and X1) will beenergized by normally closed contacts X H8 and SP as soon as the SPcontacts are returned to their normal position. If the short run is tobe in the up direction, solenoid XU will energize solenoids UP, USA, andUFA through normally open contacts XU XU and XU These solenoids will inturn energize hydraulic valve 26a, 26b, and 26c, which will acceleratethe elevator car upward at a fast rate of acceleration. When the speedof the elevator reaches approximately 150 feet per minute, contact PU ofselector switch 74 breaks and de-energizes solenoid UFA, hereby droppingout the fast acceleration hydraulic control valve 26a. The upwardacceleration then continues at a slower rate until the elevator reachesapproximately 250 feet per minute, at which time contacts EU of selectorswitch 74 breaks and de-energizes solenoid USA, which drops outhydraulic control valve 260 and stops all acceleration in the hydrauliccontrol means. The elevator then travels at approximately 250 feet perminute until it reaches the slow speed approach zone for the selectedfloor, which is indicated by the closure of a set of contacts APP whichare actuated by vanes in the elevator shaft.

The closure of contacts APP energizes solenoid X, which its correctapproach speed before it reaches the leveling circuit can comprise a setof leveling valves coupled to conduit 92 of hydraulic control means 28(PEG. .2), a

leveling valve control circuit in electrical control means In mostcases, however, itwill be latches itself closed through normally opencontacts X When solenoid X is energized it breaks normally closedcontacts X thereby tie-energizing solenoids XU and dropping out all ofthe hydraulic control valves in the hydraulic control means. Theelevator then decelerates down towards its approach speed, and thedeceleration is arrested at the approximate approach speed by the EUcontacts of the selector switch'rneans and solenoid VSU, which operateson the slow speed run just as it did on a high speed run. If the speedof the elevator is above the desired approach speed when solenoid VSU isenergized, the speed willbe pulsed down by solenoid TACZ,

which will be apparent to those skilled in the art.

herein as the selector switch means.

just as it was in a high speed approach. When the elevator enters itsleveling zone, which is the same on slow speeds as it is on high speeds,the VSU solenoid is de-energized by contact LV and the elevatordecelerates to stop at the selected floor level. The UM contacts thendrop, thus returning the valve control circuit to its originalcondition, and the leveling circuit takes over to level the elevator. Itwill be noted that deceleration relay USD is removed from the circuit bycontacts XU.; during the accelerate and constant speed portions of theshort run. This is necessary to prevent USD from being energized throughcontacts SP which are only opened momentarily in the short run. RelayUSD is, however, connected back into the circuit in the decelerationportion of the run, which is initiated by de-energizing relay XU.

The above described sequence of operation is repeated for short runs indown direction by means of the X relays and the down direction relays.On high speed runs in either direction the X relays are removed from thecircuit by normally closed contacts H8 which open at a speed ofapproximately 360 feet per minute in this particular embodiment. Duringthe short run, of course, the elevator does not have time to reach 360feet per minute and contacts H3 consequently remain closed for theduration of the short run.

From the above described sequence of operations it will be apparent thatthe valve control circuit of this invention utilizes the signals fromthe selector switch '74 to control the approximate speed conditions ofthe elevator, and that the relay meter circuits are used to makeadjustments if the approximate speeds are not within predeterminedlimits of the actual speed of the elevator car as measured by tachometer72. It will also be noted that smooth accelerations and decelerationsare achieved in part by utilizing the natural inertia of the hydraulicvalve means, which take time to move from one position to another. Therate of acceleration set by the mechanical inertia of the hydraulicvalve means can be increased artificially if desired by coupling a dashpot or the like to the stem 40 of the hydraulic valve means. It willfurther be apparent that approximate overspeed protection is provided bythe selector switch circuit per se, and that this overspeed protectionis augmented by exact overspeed protection from the tachometer and relaymeter circuits. Therefore, it will be clear that the automatic speedcontrol system of this invention provides smooth acceleration anddeceleration, equalization of speed under varying load conditions, andoverspeed protection for hydraulic elevator systems.

Although this invention has been described and illustrated withreference to a specific embodiment thereof, it should be understood thatthe invention is by no means limited to specific structure disclosedherein, since many modifications can be made in that structure withoutdeparting from the basic teaching of this invention. For example,although it is preferable to integrate the approximate speed and exactspeed control means, as disclosed herein, it is not necessary to do soin every embodiment of the invention. The approximate speed controlmeans and exact speed control means can be used independently of eachother if desired by making circuit alterations Furthermore, it is notnecessary to use the exact circuits shown herein to generate thedeceleration pulses, or to use the particular brush and Wiper structureShown A rotary selector switch can be used if desired, and the pulsatingrelay circuits could be replaced by continuously energized circuitsWithout altering the basic operation of the overspeed circuit. These andmany other modifications of the disclosed structure will be apparent tothose skilled in the art, and this invention includes all modificationsfalling within the scope of the following claims.

We claim:

1. A hydraulic elevator speed control system for use in combination witha hydraulic elevator system containing an elevator car, a hydraulic ramadapted to move said car up and down, and hydraulic valve means cou pledto said hydraulic ram to control the operation thereof, said hydraulicvalve means containing a movable member adapted to regulate the flow ofhydraulic fluid therethrough, said speed control system comprisingtachometer means coupled to said elevator to measure the speed ofmovement thereof, said tachometer means being adapted to produce anoutput signal proportional to the speed of said elevator car, thresholdcircuit means coupled to said tachometer means, said threshold circuitmeans having an oil state and an on state and being adapted to switchfrom its off state to its on state whenever the output signal of saidtachometer exceeds a predetermined value and being adapted to switchfrom its on state to its 0d state whenever the outputsignal of saidtachometer drops below said predetermined value and valve control meanscoupled between said threshold circuit means and said movable member ofsaid hydraulic valve means, said valve control means being adapted tomove said movable member in response to the on state of said thresholdcircuit means in such direction as to reduce the flow of hydraulic fluidthrough said hydraulic valve means by a predetermined amount, therebyreducing the speed of said elevator car down to a speed corresponding tosaid predetermined value of said tachometer output signal.

2. A hydraulic elevator speed control as defined in claim 1 and alsoincluding selector switch means coupled to said movable member of saidhydraulic valve means, said selector switch means being adapted togenerate output signals in response to predetermined positions of saidmovable member, said selector switch means being coupled to said valvecontrol means, and said valve control means being responsive to theoutput signals of said selector switch to retard movement of saidmovable member beyond a predetermined position thereof.

3. The combination defined in claim 2 wherein said threshold circuitcomprises a relay meter and a relay multivibrator circuit coupled tosaid relay meter, and wherein said valve control circuit includes apulser valve adapted to move said movable member when actuated, andwherein said output pulses from said relay multivibrator serve toactuate said pulser valve.

4. The combination defined in claim 3 wherein said selector switch meanscomprises an electrical switch having a fixed switch section and amovable switch section and switch contacts communicating thereinbetween,said movable switch section being coupled to said movable member of saidhydraulic valve means, and said contacts being adapted to close and toopen at predetermined positions of said movable switch section.

5. A hydraulic elevator control system for use in combination with ahydraulic elevator system containing an elevator car and a hydraulic ramadapted to move said car up and down, said elevator control systemcomprising a source of hydraulic fluid under pressure, a hydraulic fluidsink, a hydraulic control valve coupled between said hydraulic ram andsaid source of hydraulic fluid and said hydraulic fluid sink, saidhydraulic control valve having a movable member therein adapted tocontrol the flow of iydraulic fluid therethrough, said movable memberbeing movable in an up direction in which said hydraulic ram is coupledto said hydraulic fluid source and a down direction in which saidhydraulic ram is coupled to said fluid sink and having a neutralposition in which fluid flow is blocked by said hydraulic control valve,the rate of fluid flow through said hydraulic control valve beingproportional to the displacement of said movable member from saidneutral position thereof, up valve means coupled to said movable memberof said hydraulic control valve, said up valve means being operable whenenergized in a first mode of operation to move said movable memher inthe up direction thereof, and being operable when coupled to said relaymeter.

. answers.-

energized in a second mode of operation to hold said movable memberfixed in position, and being operable when de-energized to return saidmovable member to the neutral position thereof, said up valve meanscontaining a first pulser valve adapted to move said movable membertoward the neutral position thereof when energized, down valve meanscoupled to said movable member of said hydraulic control valve, saiddown valve means being oper able when energized in a first mode ofoperation to move said movable member in the down direction thereof, andbeing operable when energized in a second mode of operation to hold saidmovable met iber fixed in position, and being operable whentie-energized to return said movable member to the neutral positionthereof, said down valve means containing a second pulscr valve adaptedto move said movable member toward the neutral position thereof whenenergized, valve control means coupled to said valve means and said downvalve means, said valve control means bieng adapted to energize said upvalve means in its first mode of operation to move said elevator carupward and being adapted to de-energize said up valve means to terminatesaid upward movement of said car, said valve control means being adaptedto energize said down valve means in its first mode of operation to movesaid elevator car downward and being adapted to de-* energize said downvalve means to terminate said downward movement or" said car, selectorswitch means coupled between said movable member of said hydrauliccontrol valve and said valve control means, said selector switch meansbeing responsive to the position of said movable member and beingoperable to generate output signals at predetermined positions in tl eup and down direction of said movable member, said predeterminedpositions corresponding to approximate elevator car speeds in the up anddown direction of movement thereof, said 'valve control means beingoperable to switch said up and down valve means from their first totheir second mode of operation in respo se to said output signals fromsaid determined level and being adapted to switch from its I on state toits off state when the output signal of said tachometer drops below saidpredetermined level, a pulser circuit coupled to said threshold circuit,said pulser circuit being adapted to produce periodic output pulses inresponse to the on state of said threshold circuit, said pulser'circuitbeing coupled to said valve control means, and said val e control meansbeing adapted to energize said first and second pulser valves inresponse to the output pulses of said pulser circuit.

6. The combination defined in claim 5 wherein said up valve means anddown valve means are adapted to be energized in a plurality of sub-modesof operation in the first mode of operation thereof, each sub-mode ofoperation corresponding to a different speed of movement of said movablemember in the upward and downward direction thereof, and wherein saidvalve control means is adapted to switch said up and down valve meansfrom one sub-mode of operation to another in response to 7 outputsignals from said selector switch means.

'7. The combination defined in claim 6 wherein said threshold circuitcomprises a relay meter, and wherein said pulser circuit comprises arelay multivibrator circuit 3. The combination defined in claim 7wherein said selector switch means comprises an electrical switch havinga fixed switch section and a movable switch section and switch contactscommunicating thereinbetween, said movable switch section being coupledto said movable member of said hydraulic valve means, and said contactsbeing adapted to close and to open at predetermined positions of saidmovable switch section.

9. The combination defined in claim 3 wherein said hydraulic controlvalve comprises a hollow valve casing having a movable valve stemmounted therewithin, said valve casing having a first, second, third,and fourth openings formed therein, said first opening being adapted tobe coupled to said hydraulic ram, said second opening being adapted tobe coupled to said hydraulic fiuid source, said third opening beingadapted to be coupled to said fiuid sink, and said fourth opening beingadapted to be coupled to said up and down valve means, a first pistonmember rigidly attached to said valve stem within said valve casing,said first piston member being adapted to couple said first opening tosaid second opening when moved in a first direction and being adapted tocouple said first opening to said third opening when moved in the otherdirection and having a neutral position in which said first opening isdisconnected from all of said other openings, the degree of couplingbetween said first and second and first and third openings beingproportional to the displacement of said first piston member from theeutral position thereof, a second piston member rigidly attached to saidvalve stem within said valve casing, said second piston member having afirst face which is coupled to said second opening in all positions ofsaid valve stem and a second face which is coupled to said fourthopening in all positions of said valve stem, said first face having asmal er surface area than said second face so as to develop a net forceon said second piston member when the fluid pressure at said second andfourth openings is equal, and wherein said up and down valve means isadapted to couple said fourth opening to said hydraulic fluid source tomove said valve stem in one direction and to couple said fourth openingto said hydraulic fluid sink to move said valve stem in the otherdirection and to close said fourth opening to hold said valve stem inposition.

ill. The combination defined in claim 9 wherein said up and down valvemeans comprises a pilot valve having a second hollow valve casing and asecond movable valve stem mounted therewithin, said second hollow valvecasinghaving first, second, and third openings formed therewithin, athird piston member rigidly attached to said second valve stem, saidthird piston member being adapted to couple said first opening to saidsecond opening when rnoved in a first directionand being adapted tocouple said first opening to said third opening when moved in the otherdirection and having a neutral position in which said first opening isdisconnected from said second and third openings, said second valve stembeing coupled to said first mentioned valve stem to follow the movementthereof and being aligned with said first mentioned valve stem so as tobe in its neutral position when said first mentioned valve stem is inits neutralposition, said first opening of said pilot valve beingcoupled to said fourth opening of said hydraulic control valve, saidsecond opening of said pilot valve being coupled to said fluid sourcethrough a first normally open valve, said third opening of said pilotvalve being coupled to said fluid sink through a second normally openvalve, said fourth opening of said hydraulic control valve being coupledto said fluid source via a first normally closed valve and being coupledto said fiuid sink via a second normally closed valve, a first normallyclosed pulser valve coupled in parallel with said first normally openvalve, a second normally closed pulser valve coupled in parallel withsaid second nor mally open valve/ l. The combination definedin claim illwherein said up valve means is energized in its first mode of operationby simultaneously energizing one of said normally open and one of saidnormally closed valves, and wherem said 5 energized in its first mode ofoperation by simultaneously energizing the other of said normally openand the other of said normally closed valves, and wherein said downvalve means is switched to its second mode of operation by de-energizingsaid other normally closed valve, and wherein said down valve means isde-energized by deenergizing said other normally open and normallyclosed valves.

References Cited by the Examiner UNITED STATES PATENTS 2,913,070 11/59Nyberg l8729 3,056,469 10/62 Wilson 187-29 3,105,573 10/63 Leveski187-29 ORIS L. RADER, Primary Examiner. MILTON O. HIRSHFIELD, Examiner.

1. A HYDRAULIC ELEVATOR SPEED CONTROL SYSTEM FOR USE IN COMBINATION WITHA HYDRAULIC ELEVATOR SYSTEM CONTAINING AN ELEVATOR CAR, A HYDRAULIC RAMADAPTED TO MOVE SAID CAR UP AND DOWN, AND HYDRAULIC VALVE MEANS COUPLEDTO SAID HYDRAULIC RAM TO CONTROL THE OPERATION THEREOF, SAID HYDRAULICVALVE MEANS CONTAINING A MOVABLE MEMBER ADAPTED TO REGULATE THE FLOW OFHYDRAULIC FLUID THERETHROUGH, SAID SPEED CONTROL SYSTEM COMPRISINGTACHOMETER MEANS COUPLED TO SAID ELEVATOR TO MEASURE THE SPEED MOVEMENTTHEREOF, SAID TACHOMETER MEANS BEING ADAPTED TO PRODUCE AN OUTPUT SIGNALPROPORTIONAL TO THE SPEED OF SAID ELEVATOR CAR, THRESHOLD CIRCUIT MEANSCOUPLED TO SAID TACHOMETER MEANS, SAID THRESHOLD CIRCUIT MEANS HAVING AN"OFF" STATE AND AN "ON" STATE AND BEING ADAPTED TO SWITCH FROM ITS "OFF"STATE TO ITS "ON" STATE WHENEVER THE OUTPUT SIGNAL OF SAID TACHOMETEREXCEEDS A PREDETERMINED VALUE AND BEING ADAPTED TO SWITCH FROM ITS "ON"STATE TO ITS "OFF" STATE WHENEVER THE OUTPUT SIGNAL OF SAID TACHOMETERDROPS BELOW SAID TACHOMETER EXCEEDS AND VALUE CONTROL MEANS COUPLEDBETWEEN SAID THERSHOLD CIRCUIT MEANS AND SAID MOVABLE MEMBER OF SAIDHYDRAULIC VALVE MEANS, SAID VALVE CONTROL MEANS BEING ADAPTED TO MOVESAID MOVABLE MEMBER IN RESPONSE TO THE "ON" STATE OF SAID THRESHOLDCIRCUIT MEANS IN SUCH DIRECTION AS TO REDUCE THE FLOW OF HYDRAULIC FLUIDTHROUGH SAID HYDRAULIC VALVE MEANS BY A PREDETERMINED AMOUNT, THEREBYREDUCING THE SPEED OF SAID ELEVATOR CAR DOWN TO A SPEED CORRESPONDING TOSAID PREDETERMINED VALUE OF SAID TACHOMETER OUTPUT SIGNAL.